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Wongwiriyapan W.,King Mongkut's University of Technology Thonburi | Okabayashi Y.,Osaka University | Minami S.,Osaka University | Itabashi K.,Osaka University | And 7 more authors.
Nanotechnology | Year: 2011

Protective-layer-coated single-walled carbon nanotubes (SWNTs) with palladium nanoparticle decoration (Pd-SiO2-SWNTs) were fabricated and their sensing properties for hydrogen (H2) were investigated. SWNTs were coated with a 3-4 nm thick SiO2 layer by pulsed laser deposition and subsequently decorated with Pd nanoparticles by electron beam evaporation. Even though the SWNTs were completely surrounded by a protective layer, Pd-SiO2-SWNTs responded to H2 down to a concentration of 1 part per million. Compared with the Pd nanoparticle-decorated SWNTs without a protective layer (Pd-SWNTs), Pd-SiO2-SWNTs exhibited highly stable sensor responses with variations of less than 20%; Pd-SWNTs showed a variation of 80%. The density of the Pd-SWNTs significantly decreased after the sensing test, while that of the Pd-SiO2-SWNTs with the netlike structure remained unchanged. The hydrogen sensing mechanism of the Pd-SiO 2-SWNTs was attributed to the chemical gating effect on the SWNTs due to dipole layer formation by hydrogen atoms trapped at the Pd-SiO2 interface. Moreover, the relationship between H2 concentration and sensor response can be described by the Langmuir isotherm for dissociative adsorption. © 2011 IOP Publishing Ltd.


Itabashi K.,Osaka University | Tabata H.,Osaka University | Wongwiriyapan W.,King Mongkut's University of Technology Thonburi | Minami S.,Osaka University | And 5 more authors.
Japanese Journal of Applied Physics | Year: 2012

We fabricated single-walled carbon nanotubes (SWNTs) covered with a thickness-controlled ZnO layer (ZnO-SWNTs) by pulsed laser deposition (PLD) and investigated their UV photoresponse, induced by the photodesorption of oxygen molecules from the ZnO surface. The magnitude of the negative photocurrent and the recovery time were strongly dependent on the thickness and morphology of the ZnO layer, and were highest when the ZnO layer was 3-4nm thick. The observed recovery curves of the negative photocurrent were fitted with double-exponential-function curves, which indicate the coexistence of two types of adsorption sites for oxygen molecules on the ZnO surface. The light intensity dependence of the negative photocurrent was also measured. © 2012 The Japan Society of Applied Physics.


Itoh T.,Japan National Institute of Advanced Industrial Science and Technology | Taguchi Y.,Japan National Institute of Advanced Industrial Science and Technology | Izu N.,Japan National Institute of Advanced Industrial Science and Technology | Matsubara I.,Japan National Institute of Advanced Industrial Science and Technology | And 5 more authors.
Sensor Letters | Year: 2011

The response of CeO2 to H2S has been investigated by an alternating current (AC) impedance analysis. The AC impedance analysis can divide whole impedance, i.e., identical with direct current resistance, to three type contributions, bulk, grain boundary, and electrode interface. In a case of CeO2, the bulk contribution is the main component of the whole impedance because of clear grain boundary, which is observed by a transmission electron microscope observation. Sensor responses are defined as the quotient of sensor resistance in no odor air and sensor resistance in odor. The sensor responses of bulk contribution are almost identical with those of whole impedance. Copyright © 2011 American Scientific Publishers. All rights reserved.


Itoh T.,Japan National Institute of Advanced Industrial Science and Technology | Uchida T.,Japan National Institute of Advanced Industrial Science and Technology | Matsubara I.,Japan National Institute of Advanced Industrial Science and Technology | Izu N.,Japan National Institute of Advanced Industrial Science and Technology | And 4 more authors.
Ceramics International | Year: 2015

We developed the polyol synthesis of γ-alumina particles that allows for control of their particle size from the nanometer level to the micrometer level. The developed polyol synthesis utilized a reflux reaction of ethylene glycol solution with aluminum nitrate hexahydrate and poly(vinylpyrrolidone) (PVP). Two important process parameters - the molecular weight of PVP and refluxing temperature - were investigated to control the size of the alumina particles. Further, two growth models for amorphous alumina particles in polyol synthesis were suggested. γ-Alumina with secondary particle size ranging from 142 nm to 1.0 μm with a specific surface area ranging from 81 to 32 m2/g was obtained. The α-alumina prepared by high-temperature annealing of over 1200 °C had secondary particle sizes ranging from 246 to 330 nm, but with specific surface areas of only 5.4-11 m2/g. Therefore, it is proved that the polyol synthesis is able to control secondary particle size of γ-alumina upon maintaining a large specific surface area. © 2014 Elsevier Ltd and Techna Group S.r.l.


Kuse T.,New Cosmos Electrical Co. | Kanda K.,New Cosmos Electrical Co.
International Gas Research Conference Proceedings | Year: 2014

A new type of GC called the XG-1 00 that uses a semiconductor gas sensor to measure odorants, e.g., THT (tetrahydrothiophene), DMS (dimethyl sulfide), TBM (tertiary-butyl mercaptan) and cyclohexene, is developed. The GC is designed to use in identifying whether the gas detected by a detector is the result of leakage from underground pipelines that supply town gas or is naturally occurring gas. This GC can be used to detect between 10 ppb and several tens of ppb of THT, DMS, TBM, and cyclohexene, without sample enrichment. The device uses ambient air as the carrier gas so there is no need for highly pressured cylinder gas of N2, He, or H2, which are indispensable for normal GC systems. This is an abstract of a paper presented at the International Gas Union Research Conference (IGRC 2014) (Copenhagen, Denmark 9/17-19/2014).


Mori M.,Ehime University | Itagaki Y.,Ehime University | Iseda J.,Ehime University | Sadaoka Y.,Ehime University | And 3 more authors.
Sensors and Actuators, B: Chemical | Year: 2014

A perovskite-type SmFeO3 oxide, which has a p-type semiconducting feature, was used as a chemo-resistive sensor material for VOC detection. SmFeO3 particles were deposited on a comb-type Pt electrode printed on an alumina substrate. In this study, 15 kinds of VOCs (methanol, ethanol, propanol, butanol, acetic acid, propionic acid, methyl acetate, ethyl acetate, acetone, methylethylketone, benzene, toluene, xylene, ethyl benzene, and chlorobenzene) with concentrations below 10 ppm were examined in the range of 350 and 500 °C. The resistance of the sensor increased when the referenced air was contaminated with the VOCs. The sensing behavior was characterized by the relationship, Rvoc/Rair = 1 + αC1/m. The observed results suggested the detecting ability of ppb-levels of several VOCs. © 2014 Elsevier B.V.


Tabata H.,Osaka University | Fukuda H.,Osaka University | Matsushita K.,Osaka University | Kubo O.,Osaka University | And 8 more authors.
Applied Physics Express | Year: 2014

We found that resistive sensors using a single-walled carbon nanotube thin film covered with a SrTiO3 or CeO2 thin layer exhibit excellent responses to trace amounts (̃10-3 Pa) of oxygen. By analysis based on the Langmuir adsorption model, their responses were revealed to be due to O2 adsorption on the metal oxide layer, which involves two adsorption processes. They were assigned to identical adsorptions as superoxide species on the sites at separate locations on the metal oxide surface, i.e., at directly accessible flat areas and at recessed areas that are only accessible via thermally activated surface diffusion. © 2014 The Japan Society of Applied Physics.


Mori M.,Ehime University | Sadaoka Y.,Ehime University | Ueda T.,New Cosmos Electrical Co. | Mitsuhashi H.,New Cosmos Electrical Co. | Nakatani M.,New Cosmos Electrical Co.
ECS Transactions | Year: 2016

We examined the response behavior of SnO2 based semiconductor gas sensors to ethanol. In this study, the sensing layer was fabricated from mixed solutions of tin acidic standard solution with zinc or titanium acidic standard solution. The sensitivity of SnO2 sensors prepared from acidic standard solutions to ethanol was higher than that of metal-doped SnO2 sensors prepared from SnO2 powders. The sensitivity of Zn-doped SnO2 sensors was depressed in the humidified environment, while the sensitivity of Ti-doped SnO2 sensors was not affected by humidity even if the relative humidity was high. SnO2 films prepared from SnO2 powders composed of particles with 100 nm mean particle diameter. By using tin standard solution as a material of film, semiconductor films formed of fine particles having 10 nm mean particle diameter were obtained. This film formation method using acidic standard solutions can control the thickness of film easy, and the thin SnO2 film with around 100 nm thickness could be obtained. © The Electrochemical Society.


Patent
New Cosmos Electrical Co. | Date: 2016-04-27

A controlled potential electrolysis gas sensor including, as gas electrodes 10 for detecting gas, a working electrode for electrochemically reacting gas to be detected, a counter electrode with respect to the working electrode, and a reference electrode for controlling potential of the working electrode, the gas electrodes 10 being disposed to face an electrolysis solution accommodating portion of an electrolysis tank accommodating electrolytic solution 20. Each electrode 10 includes a noble metal catalyst layer 50. On the noble metal catalyst layer 50 of at least one of the working electrode and the reference electrode, there is formed a polymer layer 60 having ion conductivity and water permeability.


Patent
NEW COSMOS Electrical CO. | Date: 2014-06-18

A controlled potential electrolysis gas sensor including, as gas electrodes 10 for detecting gas, a working electrode for electrochemically reacting gas to be detected, a counter electrode with respect to the working electrode, and a reference electrode for controlling potential of the working electrode, the gas electrodes 10 being disposed to face an electrolysis solution accommodating portion of an electrolysis tank accommodating electrolytic solution 20. Each electrode 10 includes a noble metal catalyst layer 50. On the noble metal catalyst layer 50 of at least one of the working electrode and the reference electrode, there is formed a polymer layer 60 having ion conductivity and water permeability.

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